Experts also concluded that an outbreak of Legionnaires' Disease, an illness caused by a type of bacteria found in contaminated water systems, was likely linked to the city water supply.

In 2014, while Lyon was still HHS Director, Flint changed its primary water source from Lake Huron to the Flint River to cut costs. The charges stem from an investigation led by Michigan's attorney general.

Others charged with involuntary manslaughter on Wednesday included former state-appointed emergency manager Darnell Earley, former Flint city employee Howard Croft, and former state Department of Environmental Quality officials Stephen Busch and Liane Shekter-Smith.

December 2: Researchers report that water in Flint is improving after finding no detectable levels of lead in 57 percent of homes during another round of tests. Lead from old plumbing leached into the water system.